Surgeons have implanted leads into the coronary sinus of the heart of a patient by using one of two methods to drive and position the lead. One method is to utilize a stylet to push the lead tip through the venous system when the stylet is fully inserted into the lead. The other method is to slide the lead over a guidewire. The lead has openings at each end through which the guidewire passes. The guidewire is positioned into the coronary sinus and the lead is then moved into position by sliding over the guidewire. Each method has its benefits. The problem is that, previously, it was necessary for the surgeon to choose which method to use prior to surgery.
Also, cardiac pacing and/or defibrillation leads are constructed generally using any of the following materials: silicone rubber, polyurethane, coil windings, cables with or without ETFE coating, and PTFE tubing. The lead is generally designed so a stylet can pass through the coil winding or PTFE tubing. The surgeon can then drive the lead into the desired location inside the heart using the stylet.
However, there are risks that are inherent to the procedure just mentioned. The lead must follow the venous system of the body and can experience very tight and tortuous bends. These bends can create a strain on the lead and require a greater force to drive the lead. The stylet then has the risk of passing in between the coil windings of the lead or piercing the PTFE and perforating the lead. This perforation is dangerous to the patient. Tearing of the veins or cardiac tamponade is a distinct possibility.
Typical of the known prior art are U.S. Pat. Nos. 5,807,339 and 5,728,148 to Boström et al. and U.S. Pat. No. 5,722,425 to Boström, each of which discloses a stylet unit which can be introduced into a hollow, flexible, component such as an electrode cable for a heart stimulator, to stiffen the component and to bend a distal end section, is in the form of a double stylet combination with a flexible tubular stylet shell and an internal stylet, movably arranged inside the shell, with a pre-curved distal end section, whose radius of curvature is on a first side of the stylet.
U.S. Pat. No. 5,935,160 to Auricchio et al. and U.S. Pat. No. 5,803,928 to Tockman et al. both disclose implantable lead systems which can be implanted by either a stylet or a guidewire.
It was in light of the foregoing that the present invention was conceived and has now been reduced to practice.